Not all of these sites will help all levels of math, and some sites are more appealing to parents and teachers than to kids... it's just a menu... pick and choose...
xtramath.org Elementary level. Timed skills practice. Keeps track of progress. (Abby likes it.)
www.mrnussbaum.com Elem/Middle level. Good games for many subjects- not just math.
www.thinkingblocks.com Grades 3 - 8 THE BEST SITE for problem solving and visual thinking. You will enjoy working through the problems with your kids.
www.mathplayground.com Elem/Middle level. Lots of math games.
National Library of Virtual Manipulatives Parents should get familiar with this site- especially if they homeschool. Lots of different math activities. You DO NOT have to download or purchase- you can use it straight from the site.
www.coolmath.com and www.coolmath4kids.com Good explanations of math topics from fractions to algebra and beyond- even finance. Lots of links and games.
www.teachertube.com Hundreds of thousands of videos with all levels of math explanations. Some are excellent, some are dismal. Parents might want to weed through to see what is useful.
www.khanacademy.org Instructional videos on many topics.
www.ixl.com Pre-K to Algebra. First 20 problems per day are free. Subscription gives access to hundreds of practice problems by grade level and state standards. Well worth the price. Keeps track of progress, good communication with parents.
www.indianmathonline.com Grades 1- 10. (I have no personal experience with this program, but it appears valid and has three different levels of subscription.)
Of course, you can do an internet search and see how many other sites will help you with your math, but these are good starting places- especially if you don't have a lot of time to spend searching.
Best wishes to you for an excellent school year!